As an AMO editor reviewing comments from users I often see reviews which simply state "{Addon name} doesn't work with {application version #}" and nothing else. Being able to go quickly to the extension's info page and looking at the range the extension is supposed to work with can help weed out the truly confused people who are trying to use the extension on the wrong version. Even though there is now the "download" button if the user agent string is correct, I have no doubt that being able to see the version range would still be of use to many people for little things like this.

Verified dup (Hi, Lukas!)